Automotive electronics are different than consumer electronics. For automotive electronics, every integrated circuit (IC) must be tested for electromagnetic compatibility, commonly referred to in the art as “EMC testing.” EMC requirements are much less stringent for consumer electronics than for automotive electronics. More specifically, an IC should not introduce too much noise in its supply lines or bus lines through parasitic inductance. When current (di/dt) is introduced through the supply side of an IC too quickly, the IC may experience a significant amount of voltage noise due to the parasitic inductance in bonding wires. For automotive electronics, such noise may result in a faulty or damaged IC.
The trend toward lower power, portable equipment has driven the technology and the requirement for converting power efficiently. Modern IC switching regulators are small, flexible, and allow either step-up (boost) or step-down (buck) operation. Switching regulators are commonly preferred over traditional linear regulators because of their characteristic high efficiency and high power density stemming from smaller magnetic, capacitive, and heat sink components. These switching regulators may be constructed from various arrangements of a switch, a diode, an inductor, and a capacitor.
The primary limitations of switching regulators as compared to linear regulators are their output noise, electromagnetic and radio-frequency interference emissions, and the proper selection of external support components. EMC is one of the basic requirements for electronic control units, and low conducted emission testing is essential for the development of ICs to make sure noise in battery or supply lines is well controlled. One particular type of switching regulator, a buck switching regulator, uses two power switches, such as power metal-oxide-semiconductor field-effect transistors (MOSFETs), to selectively couple an inductor to a high power supply and a low power supply. Fast switching currents in switching regulators introduce voltage ringing at bonding wires due to parasitic inductance. For instance, a 2 nH parasitic inductance in bonding wires with 1 A of lead current every 2 ns will produce voltage ringing of 1V, as indicated in the following equation:V=L*di/dt=2 nH*1 A/2 ns=1V.
To reduce voltage ringing, either the parasitic inductance or the current slew rate needs to be reduced.
One traditional way to reduce parasitic inductance in a switching regulator is to connect multiple bonding wires between the voltage supply and the high-side switching regulator MOSFET and the low-side switching regulator MOSFET and ground. But use of additional wires takes up costly space on an IC and may require additional chip pins, both of which raise costs of an IC.